During the operation no stipulations are made regarding the anaesthetic technique to be used, which is left entirely at the discretion of the anaesthetist with clinical responsibility for the patient. In the last 30 minutes of the operation, the patient's artificial ventilation will be with an oxygen concentration of 40% and a set 'positive end expiratory pressure'(PEEP). Other than that, anaesthetists will be free to wake the patient up by their own preferred method. Also, if at any time the responsible anaesthetist feels the adjustment of the ventilation is required in order to act in the patient's best interest, the patient will be removed from the trial.